1. Field of the Invention
The present invention relates to an image pickup apparatus, such as an electronic still-image camera having a focus adjusting function, or the like, an image pickup method, and an image-pickup control computer program.
2. Description of the Related Art
Conventionally, in electronic still-image cameras, video cameras and the like, methods have been used in which a lens position where a high-frequency component of a luminance signal obtained from an image pickup device, such as a CCD (charge-coupled device) or the like, is maximized is made an in-focus position. Among such methods, a mountaineering method in which a lens is moved in a direction to increase a high-frequency component of a luminance signal (hereinafter termed a “focus evaluation value”) obtained from an image pickup device, and a position where the focus evaluation value is maximized is made an in-focus position, and a scanning method in which focus evaluation values are stored by moving a lens over the entire range region, and a lens position corresponding to the maximum value of the stored values is made an in-focus position have been known.
Usually, in these methods, as shown in FIG. 15, a central portion of a photographing picture frame is used as a range frame, and a lens position having a maximum focus evaluation value for an object within the range frame is made an in-focus position. A method has been known in which, as shown in FIG. 16, a plurality of range frames are set, and after storing focus evaluation values for the respective range frames, a lens position corresponding to the maximum value of the focus evaluation values for each of the range frames is obtained, and a position where a lens is to be finally moved is determined from among these lens positions. The relationship between the lens position and the focus evaluation value obtained in the above-described manner has the shape of a mountain as shown in FIG. 17.
When objects at different distances are absent within the range frame as shown in FIG. 15 or FIG. 16, the relationship shown in FIG. 17 is obtained. However, when objects at different distances are present within the range frame, the relationship between the lens position and the focus evaluation value is as shown in FIG. 18. That is, a peak of focus evaluation values is present for each of the objects at the different distances. Accordingly, when objects at different distances are present within a range frame, peaks appear at two different lens positions, as shown in FIG. 18.
In such a case, since it is impossible for a camera to determine on which object the photographer intends to focus, the lens is in most cases moved by selecting a position corresponding to the closest distance from among a plurality of peak positions. In such an approach, however, for example, when photographing an image across a wire netting, the wire netting is focused instead of an object intended by the photographer to be focused. Even if the camera is not focused on the closest position, it is impossible for the camera to determine to be focused on a position intended by the photographer.